So-called horizontal sliding doors include at least one door panel that is suspended by a carriage that travels along an overhead track. The door panel may be manually or automatically moved from a blocking position to an unblocking position along the overhead track. Wider door openings are often spanned by having two bi-parting door panels. In some instances, the amount of overhead track required to extend beyond the door opening is reduced by having the door panel vertically divided into a number of coupled (e.g., over-lapped, hinged) vertically-separated leaves that take up less horizontal space when moved to the unblocking position.
Cold storage lockers are often accessed through a door opening closed by a sliding door. The panels for this purpose are typically transparent vinyl sheets, minimally insulated flexible panels or foam filled rigid panels. The transparent vinyl sheets are selected to reduce the likelihood of damage to the door. In particular, such doors are used in institutional (e.g., warehouse) setting wherein palletized cargo is moved in and out of a cold storage locker by forklift. Another advantage to these doors is that forklift operators can see what is on the other side of the door before opening the door. Although providing damage resistance, these types of panels have a very low insulation value and are too flexible to provide an effective air seal between the environments on either side of the opening. Because of the properties of the material, the transparent vinyl sheets may develop a warp that prevents a good seal. Air pressure differentials will cause leakage due to the lack of a compressive seal between the door panels and the doorframe. This will allow a significant amount of warm moist air to enter the cold storage locker and/or refrigerated air to be lost into an unrefrigerated space. Consequently, such door systems are less efficient to operate and can suffer from ice accumulation in the cold storage locker.
Rigid door panels are often used, especially in the United States, in order to reduce the operating costs of a cold storage locker. The rigid panel provides a consistent surface to seal to the doorframe. The thickness of the rigid door panel is selected to provide a specific amount of insulation. While these rigid door panels provide an effective closure, impact by a forklift can cause damage to the door system that would make them inoperative and limit access to the cold storage locker.
Attempts have been made to provide a damage resistant door panel for a sliding door system that also provides sufficient insulation. Resilient door panels have been suggested which have sufficient thickness to insulate like a rigid door panel, but yield to a degree when impacted by a forklift. While the panel itself achieves a degree of insulation, the insulation capability of the overall door system suffers from poor sealing between panels and poor sealing between a panel and the doorframe. Specifically, the stiffness of each door panel tends to be less than that of a rigid door panel, and thus presents less of a compressive contact to a doorframe gasket to achieve a seal. To achieve a seal with this type of panel different devices have been tried. Interlocking gaskets can be damaged as the door is pulled away from the casing. In addition they require rigid plates in the door panel for attachment which makes the panel heavier and less resilient. Others have used wall mounted guide tracks to pull the middle of the door back. This adds additional cost, makes installation more difficult and does not address sealing of the entire edge of the door; it only forces a seal at the top, bottom and middle. Because of the application it is difficult to add electrical wiring to the panel because it is flexible and could be torn open and damage or expose wiring. Condensation control on the panel is typically done using resistance wire but that will does not work because of the panel design. Others have tried using external heaters and blowers that are an inefficient means of controlling the condensation.
Consequently, a significant need exists for an improved door system that is suitable for institutional cold storage lockers by providing significant thermal insulation, efficient condensation control yet being resistant to damage from impacts.